porting

[joey4346]

I hav a few questions. What is the stock piston's compression ratio? and can head porting be a done correctly by an amatuer?? if so can anyone give me some tips.

[buster369]

head has to be ported by someone that knows what they are doin cause the valuve seats can't be damaged. compression on what 400? 300?

[joey4346]

on a 400

[buster369]

i'm not sure so don't quote me but somewhere around a 10:1

[mojoe2878]

its 9.1:1

[DaleJrFan]

dont try to port it yourself unless you know exactly what you are doing, you can jack up your valves real quick that way.

[khen]

I ported and polished my own head. I just looked at a few pictures I found online and copied those. I opened my intake quite a bit and matched the intake boot to the port and also opened the exhaust quite a bit and polished it and I'm very pleased with the results. Here is a good picture(albeit a little sloppy) of a mild port job on an XR400 engine. http://4strokes.com/tech/honda/xr4engwk/

You want to polish the exhaust ports but leave the intake ports a little rough.

Just be very carful not to nick your valves(if you leave them in) and make sure to clean all the metal filings out of the ports when you're done or they could damage your valve seals.

BTW: If you decide you don't want to do the port/polish work yourself you can talk to mikeboone on this forum, he has reasonable prices on what looks like great work.